U.S. Pat. No. 2,497,893 shows a synchronized and adjustable safety clutch having a driven shaft and a driving shaft. If an overload is imposed on the driven shaft or an obstruction encountered by the machine, pin 15 is forced out of its cavity 8 thus forcing the movable clutch member 9 backward against springs 11 and stopping the machine. If this occurs the safety pin 22 will be forced into its recess 22 on shaft 2 thereby locking the clutch member in retracted position.
U.S. Pat. No. 3,282,387 teaches an overload clutch of the detent type. A motor has a driving plate secured to the shaft. The driving plate is bolted to a detent carrying plate. A driven plate is secured in the driving plate along with a wear plate. A detent or plunger is heldin the carrying plate and is urged by a spring towards the wear plate. The detent is at+ached to a detector plate. When there is overload, the detent urges the detector plate o contact another plunger which activates a microswitch to shut off the motor, and thus disengage the clutch.
U.S. Pat. No. 4,117,652 teaches a transmission for self propelled walking lawn mowers. A lever is grasped and pulled by an operator of the mower. This action pulls on a cable to move another lever in a clockwise direction. The shifter fork is then moved to the right to cause the clutch dog to engage the worm wheel. When the manually operated lever is released by the operator a spring returns the shifter dog to the left and disengages the power wheels from the engine,.
U.S. Pat. No. 4,205,509 teaches a power transmission device for a power operated lawn mowing machine. A rotational shaft for a motor and a rotational shaft for a cutting blade are interlocked with a friction clutch. These clutches become engaged and disengaged, by a manually operated lever. A disc brake also applies braking action to the cutting blade at the time of clutch disengagement
U.S. Pat. No. 4,466,233 shows a mower drive assembly for selectively coupling an engine drive shaft to rotatably drive a mower blade by grasping a control lever or halting the blade when the control lever is released while the engine is running. The drive assembly includes a drive member secured to the end of a drive shaft and supporting an annular driven member to which the mower blade is connected. A clutch ring is coupled for rotation with the driven member by intermeshing sets of teeth movable axially relative to each other to accommodate spring biased axial clutch ring displacement with a brake pad to halt driven member rotation. An activator yoke responsive to control lever retraction displaces the clutch ring from the the pad and into engagement with the driven member for rotation thereof.
U.S. Pat. No. 4,593,800 is directed to a clutch mechanism that can have its bias changed so that it is independent of the torque applied to the clutch. A drive ,shaft is connected to a driving element. A driven element is connected to the driving element through bearings. Bores in the driving shaft contain a set screw to adjust the bias of a spring connected to a moving element. Hemispherical indentations in the driven element receive the moving member. When the torque on a driving member exceeds its limit, the movable members is compressed and activates a warning pin whereupon another movable member is engaged to drive the driven element. If the torque on the driving element is increased to excess both movable members become disengaged Then the pin signals overload and the driven element is stopped from operating.
U.S. Pat. No. 4,746,320 teaches a torque limiting clutch having a driving member and a driven member. The driving member has slots for accommodating a series of ball detents with spring and adjustable nut biasing against the detents forcing them into a seating relationship on bearing seats provided on a rotatable member integral with a driven member. Various races are biased against the ball detents to insure distribution of uniform pressure and provide freedom for shifting of the detents as they are unseated during clutch disconnection. A displacement plate connected to the races is shiftable when the clutch disconnects to actuate a microswitch for shutting off operations when excess torque has been encountered.
The art teaches that there are a number of overload clutches of the detent type. Some clutches use ball type detents and some have an adjustable feature using screws. When an overload occurs the clutches are designed to disengage and activate a switch so that the entire assembly ceases operation. In the case of some lawnmowers the clutch becomes disengaged so that the blade ceases to rotate while the motor continues to run; however, it is necessary that an operator manually grasp a control lever to control the sequence of events. Furthermore, a brakepad is also required to brake the blade at the time of clutch disengagement.
It is an object of this invention to produce a safety device for a walking motor driven lawnmower which is simple in design and relatively inexpensive.
It is a further object of this invention to design a safety clutch for a motor driven lawnmower which requires no control lever requiring an operator to inactivate the blade while the motor continues to run.
It is still an object of this invention to produce a safety clutch for a power operated lawn mower wherein the mower blade becomes reoperable once overload has been overcome without restarting the motor.
It is an additional object of this invention to adapt a safety clutch for a manually operated lawn mower that requires no additional accessories such as a brake to halt the blade once the clutch has been disengaged.